Exploring the Moon

The Apollo missions, sending men to the Moon, is considered the greatest feat of mankind. NASA , National Aeronautics and Space Administration, was formed July 29, 1958 for the purpose of putting a man on the moon. NASA's motto was "For the benefit of all"

In the Apollo 11 mission, eleven years later on July 20, 1969, Neil Armstrong and Buzz Aldrin walked on the Moon, with Michael Collins orbiting above.

Neil Armstrong snapped this photo of Buzz Aldrin setting up a seismograph during the first trip to the Moon

The astronauts set up a seismograph to record moon-quakes. A mirror was set up to reflect laser pulses to record changes in the distance to the moon. Almost a ton of Moon rocks and soil were collected by the Apollo program for analysis. The Apollo 11 crew left these instruments and a plaque with the inscription "We came in peace for all mankind."

The Moon Is Not Made of Green Cheese

The Moon is much like the early Earth. It has basalt, lava-like rocks produced by melting, and breccia, aggregates of rocks pressed together during impacts, and many other types of rock.

While the Moon may not be made of green cheese, its surface is covered with dust made of green powdery glass spherules as well as abrasive powdery shards of glass.

Lunar dust: green glass spherules

Abrasive powdered glass dust

Green and orange glass spherules were collected from the Apollo 15 landing site at Hadley Rille on the Moon. These samples are volcanic deposits formed early in the Moon's geologic history. Gasses trapped in them enabled scientists to follow the history of lunar cratering over the last 3.5 billion years, showing that the rate of impacts declined to a minimum about 400 million years ago, just when life on Earth flourished. Recently they were analyzed again, and their contents revealed that the early Moon was rich in water.

The abrasive dust was an unexpected challenge to the astronauts. Not only did it wear partially through the outer gloves of their space suits, but it stuck to everything with static cling.

If surface glass could be melted, it could be used to construct buildings and telescope lenses on the Moon. The Moon's 15-day night and absence of atmosphere would make the Moon ideal for optical telescopes, The far side of the Moon, protected from radio signals from Earth, is good for radio telescopes, The poles of the Moon would be useful for a space station from which to launch missions to Mars and beyond.

Water and Warmth for Living on the Moon

Comets are "dirty snowballs", and when then strike planets and the Moon, they leave behind water ice. Most of the water vaporizes and is split by sunlight into hydrogen and oxygen. The Moon's gravity is too weak to hold onto this these gases. Solid ice might remain, protected in deep craters near the poles such as Shackleton crater shown here.

Shackleton Crater, 19 km across, may have water ice

Clementine, while mapping craters at the lunar south pole in 1994, found that up to 14,000 km² might be in permanent shadow. The Clementine mission radar was directed down to the Moon's poles, and scattered radar energy was detected by NASA receivers on Earth. The experiment revealed small, frozen pockets of water close to the surface. As Lunar Prospector orbited the Moon in 1998 and 1999, its neutron spectrometer indicated that high concentrations of hydrogen were present in the upper meter of the regolith near the polar regions. Estimates were made based on these signals that there is more than a cubic kilometer of water ice in the lunar soil near the poles.

In daytime sunlight the Moon's surface is above the boiling point (100 C), sometimes as much as 123 degrees Celsius, while in the shadow of night the surface temperature is -233 degrees Celsius. Peaks at the poles would have sunlight on one side and shade on the other. By routing pipes beneath warm and cool surfaces, these could provide geothermal heat and cooling.

A Day on the Moon: Phases of the Moon

We would want to arrive during the Moon's daylight hours. Since the same side of the Moon always faces Earth, the Moon rotates once for each time it circles Earth. We can see by the Moon's phases that the lunar day is about 30 Earth days.

Look at the Moon at sunset each night, starting with the first crescent. Each successive night begins with the Moon a little further east. Can you tell that the Moon is orbiting Earth in the same direction Earth is rotating, only much slower?

At sunset the first crescent always appears furthest west, the "quarter" Moon appears highest, and the "full" Moon rises in the east as the Sun sets in the west

Like the Sun, the Moon rises higher in some seasons, and changes where it rises along the horizon during the seasons. But the Moon's motions are less predictable than the Sun's, since the Moon's orbit tilts from the plane of the solar system by about 5 degrees, and the Moon's orbit wobbles (precesses) like a slowing top once every 18.5 years.

The Moon's most northerly northern full-moonrise happens only once every 18.5 years. In between, after about 9.25 years, is the Moon's most southerly full-moonrise. The times when it is most central are every 4.75 years, or every 56 months.

Oddly enough, there are 56 Aubrey Holes at a mysterious 5,000 year old prehistoric monument called Stonehenge!

The Mystery of Stonehenge

Stonehenge

Stonehenge, rising from Salisbury Plain in southwestern England, dates from at least as early as 3,100 BCE. Its axis of symmetry, marked by central trilithon and the heel stone, align with the sunrise on the summer solstice, when the sun rises furthest north.

Sunrise at Stonehenge

The 30 standing stones in a ring match the number of days in the lunar month.

Unlike the Sun, the Moon rises furthest south in summer and furthest north in winter. How far north and south changes because the plane of the Moon's orbit is inclined to the plane of the Earth's orbit, and rotates around once every 18.5 years. In some years, the rising and setting points of the Moon go further north, in other years further south.

There are 56 Aubrey Holes at Stonehenge. This is approximately the number of months that pass for moonrises to swing through a complete cycle, from most northerly, to nearest the Sun, to most southerly, to nearest the Sun, and back to most northerly moon-rise again.

Alignments of moon rise and set, and sun rise and set, at Stonehenge

It has been suggested the monument was built to predict solar eclipses. Eclipses are most likely to occur when Sun and Moon are closest to the points where their paths through the sky cross.

Lunar Eclipses Only Happen During Full Moons

Tides

The highest tides, spring tides, occur during full and new moons, since the Moon and the Sun both pull on the oceans. High tides, pulled mostly by the Moon alone, are called neap tides.

Even though the mass of the Moon is relatively small, and only has a sixth the gravity of Earth, the Moon has more influence over the tides than the Sun, because the Sun is vastly further away.

Newton's formula for gravitation

It may seem odd that Earth has two high tides at the same time. This is because the Moon's pull is so much less on the far side of the Earth, due to the increased distance "r" in this equation.

Tides near and far are due to increasing distance

The oceans nearest the Moon are pulled more than the center of the Earth, which is pulled more than the oceans on the far side. With respect to the center of the Earth, it is as if oceans are pulled in opposite directions. As the Earth rotates under the ocean's bulge, it experiences two tides each day. The height of the tide depends upon the position of the Moon relative to the Sun.

The tides aren't exactly beneath the Moon, because as the Earth rotates, friction drags the oceans with it. As a result the high tide follows about 12 minutes after the Moon is highest overhead.

Friction from the Earth pulls tides slightly east of being directly below the Moon.
The tides follow the overhead Moon by about 12 minutes.

The most pronounced tides in the world are at the Bay of Fundy at the Lawrence River in Nova Scotia, Canada. Every year a "Not Since Moses Race" is held. Biblical accounts of Moses parting the Red Sea are strikingly similar to this annual event.

High and Low Tides in the Bay of Fundy Nova Scotia

The Reversing Falls at the Bay of Fundy changes directions according to Moon and tides, sometimes making fierce waves and whirlpools.

A quiet moment at the Reversing Falls by the Bay of Fundy, Nova Scotia

Origin and Fate of the Moon

Like the orbits of the planets, the Moon's orbit is elliptical, sometimes closer, and other times further from the Earth. According to the laser reflector placed on the Moon by the Apollo astronauts, the mean (average) distance to the Moon is moving away Earth at speed of about 3.8 centimeters (1 1/2 inches) per year.

If this movement away from Earth were always the same, measuring backwards, the Moon would have been at the Earth in its formative years, about 5 billion years ago. The composition of the Moon is much like the Earth's outer mantle, but lacks any iron core. This suggests the Moon was part of Earth at some time.

Some say a collision with a huge meteor could have knocked a giant piece off the side of the molten Earth. Or the Earth could have been an irregular blob, and thrown off part that became the Moon. Or the Moon could have been captured, but that would not explain the lack of an iron core.

Since the composition of the Moon is similar to the Earth, except it lacks any iron core, present theory is that it was blasted off the surface of the Earth by a giant asteroid. The Earth would have still been in a molten state then, but the iron would mostly have sunk to Earth's core. The debris of the collision reassembled around the Earth to make the Moon. Simulations of potential impacts have identified that an one capable of forming an Earth-Moon system is of Earth at the end of its formation with Mars-sized object, about 4.5 billion years ago.